The hydrolysis of meat with industrial enzyme preparations, such as proteinases, for the purpose of producing a protein hydrolysate or a flavor-imparting meat extract is disclosed in the state of the art, for example, in WO 94/01003, EP-A 505 733 and DE-A 28 41 043. The use of alkaline or neutral endopeptidases, such as Alcalase (NOVO) or Pescalase (GIST), of bacterial origin for the purpose of producing oligopeptide-rich hydrolysates from plant proteins, and also whey proteins and egg proteins, is also described, for example, in EP-A 511 970. The use of an endopeptidase and exopeptidase enzyme preparation (Flavorzyme) (NOVO), which is obtained from fungi, is described in WO 94/25580. In this case, protein hydrolysates having a relatively high degree of hydrolysis are produced from plant proteins and also from fish proteins and meat proteins, including gelatin.
The enzymic hydrolysis of protein from meat adhering to bones is well known in the state of the art and is nowadays carried out in meat-processing concerns with the aim of ensuring that residual material is fully utilized. This is known, for example, from H. Uhlig, Enzyme arbeiten fur uns (Enzymes work for us), 1991, Hanser Verlag, pp. 325 ff., J. Adler-Nissen, Enzymic Hydrolysis of Food Proteins, 1986, Elsevier Appl. Sc. Pub., pp. 90 ff. or Behnke et al., Nahrung, 28: 397-407, 1984. Residual materials from fish processing can also be used, with it being possible to use the fish's own enzyme system, as described in EP-A 535 135.
A fundamental problem in the enzymic hydrolysis of animal protein is the formation of a bitter flavor due to peptide fragments. In order to solve this problem, the state of the art proposes, for example in EP-A 223 560, employing proteolytic enzyme combinations consisting of endopeptidase and exopeptidase mixtures and aminopeptidases for degrading the resulting bitter tasting peptides. Furthermore, WO 94/01003, proposes adherence to a given degree of hydrolysis and the use of raw meat instead of the boiled commodity. DE-A 30 03 679 proposes masking the bitter-tasting substances with additives such as carbohydrates. Possibilities of avoiding or masking the bitter flavor are discussed in Food Technology, 48: 96-98 (1994).
The enzymic hydrolysis of collagen-rich material, for example gelatin, is likewise disclosed. The products which are obtained in this case are not so bitter as those obtained during the enzymic hydrolysis of meat. However, in this case, it is often only a partial hydrolysis of the protein, with a low degree of degradation, which is sought. The possible enzymic hydrolysis of rind and bones for the purpose of obtaining gelatin would be such an application. However, this application has up until now not been able to compete with the traditional disruption with acid and alkali because it is difficult to control the degree of hydrolysis precisely. The impression that enzymic gelatin hydrolysates have a flavor which is less bitter is due, inter alia, to the proportion of free amino acids which are possessed by collagen-rich material which do not taste particularly bitter. In particular, this material contains sweetly tasting amino acids such as glycine and less bitter tasting arginine.
Experiments for preparing hydrolysates from collagen-rich material are described, inter alia, by Lin and Chen, Proc. of AAAP 2: 1112-1114 (1985) and in JP-A 52 110874 and JP-A 52 099265. Collagen-rich hydrolysates can be obtained commercially (Marggrander, Fleischwirtschaft 75: 1286-1287 (1995)).
A hydrolysate prepared from collagen is also described in DE-A 25 37 618. In this case, a non-bitter product having a molecular weight of greater than 2000 daltons is obtained by hydrolysis in the alkaline range. DE-A 36 20 150 describes a collagen hydrolysate in the molecular weight range of 15,000 daltons as a replacement for common salt. U.S. Pat. Nos. 4,130,555 and 3,743,514 propose collagen hydrolysates prepared from gelatin and rind for protein enrichment in sausages.
However, if an attempt is made to hydrolyse protein-containing animal products, in particular raw or boiled pork rind, with this latter also being a collagen-rich material, for example using endopeptidases in this way, it is observed that, from a particular hydrolysis time onwards, markedly bitter tasting hydrolysates are to be expected, both in the case of the raw commodity and in the case of the boiled commodity, as the degree of hydrolysis increases. The bitterness can only be forced below the perception threshold when the degree of liquefaction is quite low, i.e., when the hydrolysis time is short, and when assisted by common salt, which serves to mask the bitter taste. The same problem arises when air-dried rind is hydrolysed. It is also found that hydrolysates prepared from fresh ham taste astringent, bitter and acid irrespective of whether the ham is raw or boiled.
Consequently, an object of the invention is to make available a process for preparing a protein hydrolysate which, even without masking and despite a high degree of liquefaction and a long hydrolysis time, does not taste bitter and which consequently constitutes an advantageous flavorant.